The expression of water- and oil-repellency results from the low surface energy of fluorine, and, usually, fluorine-containing acrylate polymers are widely used as active ingredients of water- and oil-repellents. Previous various investigations have shown that the presence of crystallinity in a fluorine-containing polymer is necessary for expressing water- and oil-repellency in practical applications. In particular, it has been recognized that the hydrophobicity of a fluorine-containing polymer depends on the number of carbon atoms of a side-chain fluoroalkyl group and that the expression of crystallinity is observed when the number of carbon atoms is eight or more.                [Non-Patent Document 1] Secchaku (Adhesion), Vol. 50, No. 5, pp. 16-22 (2006)        
Therefore, it has been regarded that a fluorine-containing polymer having a short fluoroalkyl group, i.e., a side-chain fluoroalkyl group having 7 or less, in particular, 6 or less carbon atoms, is low in or does not have crystallinity and thereby cannot provide water-repellent performance that is sufficient for practical use. In addition, since water and oil-repellents are required to have washing resistance and abrasion resistance, fluorine-containing acrylic polymers having long side chains are used.
However, polymers including a side-chain fluoroalkyl group having 8 or more carbon atoms are very hard due to their high crystallinity and have a problem that flexibility of textile products is impaired. Furthermore, since the water-repellent process needs high curing temperature, there are problems such as a change in color of fibers. In addition, since a long side-chain having 8 or more carbon atoms is excessively hydrophobic, a large amount of an emulsifier is necessary for producing a water- and oil-repellent.
The present applicant has before proposed a water and oil-repellent composed of an aqueous emulsion in which a copolymer of a fluoroalkyl group-containing polymerizable monomer and vinylidene chloride or benzyl (meth)acrylate, and a carboxyl group-containing water-soluble polymer are dispersed in water using a nonionic surfactant. The fluoroalkyl group of a fluoroalkyl group-containing polymerizable monomer that is copolymerized with vinylidene chloride or benzyl (meth)acrylate is recognized to be a perfluoroalkyl group having 4 to 20 carbon atoms, but the perfluoroalkyl group used in the above-mentioned polymerization example is recognized to be a mixture of perfluoroalkyl groups having 6 to 14 carbon atoms, 9.0 on average.
[Patent Document 1] JP-A-11-80710
Furthermore, as a water-dispersible water- and oil-repellent composition in which both the repeated washing resistance and the water pressure resistance of water- and oil-repellency are achieved, a water-dispersible water- and oil-repellent composition including as active ingredients (A) a fluorine-containing copolymer having a hydroxyl group, (B) a fluorine-containing copolymer having an epoxy group, (C) a compound having a blocked isocyanate group and not having a carbon-carbon unsaturated bond, and (D) an amino resin has been proposed. The fluorine-containing copolymers having the hydroxyl group or the epoxy group are each a copolymer of a polymerizable monomer having a polyfluoroalkyl group, wherein the number of carbon atoms of the perfluoroalkyl group of a perfluoroalkylalkyl group is 2 to 20, preferably 6 to 16. A perfluoropentyl group and a perfluorohexyl group are shown as examples, and in the Examples, a mixture of F(CF2), groups of which m is from 6 to 16 and is 9 on average is used.
[Patent Document 2] WO 00/58416
Accordingly, it is believed that a water- and oil-repellent showing excellent in flexibility and also excellent in washing resistance can be obtained if water- and oil-repellency can be expressed with a fluorine-containing polymer including a short fluoroalkyl group having 6 or less carbon atoms.
Furthermore, acrylic acid derivatives of perfluoroalkylalkyl alcohol, for example, CF3(CF2)7CH2CH2OCOCH═CH2, are widely used as synthetic monomers for fluorine-containing copolymer that forms a water- and oil-repellent for fiber, but recently, it has been reported that among these types of compounds, compounds including perfluoroalkyl groups having approximately 8 carbon atoms are high in bioaccumulation potential and therefore have an environmental problem. Accordingly, it is concerned that the manufacturing and the use of these compounds will become difficult in the future. However, compounds including perfluoroalkyl groups having 6 or less carbon atoms are recognized to be low in bioaccumulation potential.
It has been also proposed a surface-treating agent showing excellent water repellency, oil repellency, and antifouling property by using a polymer having a short fluoroalkyl group having 1 to 6 carbon atoms as the side chain, but the fluoroalkyl group-containing monomer used therein is a fluorine-containing monomer compound represented by the general formula:Rf-Y—O—CO—CX═CH2                 X: F, Cl, Br, I, CFX1X2, CN, a fluoroalkyl group having 1 to 20 carbon atoms, benzyl group, or phenyl group,        Y: an aliphatic group having 1 to 10 carbon atoms, an aromatic or alicyclic group having 6 to 10 carbon atoms, a CH2CH2NR1SO2 group, or a CH2CH(OY1)CH2 group, and        Rf: a fluoroalkyl group having 1 to 6 carbon atoms.Acrylic acid derivatives in which X is H are shown as comparative manufacturing examples, and methacrylic acid derivatives in which X is CH3 are intendedly excluded.        
[Patent Document 3] JP-A-2004-352976
Furthermore, it has been proposed a water- and oil-repellent composition of which essential component is a copolymer containing as a polymerization unit (a) an Rf group-containing monomer of which homopolymer does not have a melting point derived from the Rf group in the microcrystals or has a melting point of 55° C. or less and has a glass transition point of 20° C. or more and (b) an Rf group-free monomer having a cross-linkable functional group, wherein the composition can impart excellent water- and oil-repellency to products, even in low temperature treatment, and also can perform a water- and oil-repellent process with providing soft textile feeling and also excellent durability.
[Patent Document 4] WO 2004/035708
In the above, a perfluoroalkylalkyl (meth)acrylate is used as the component monomer (a), but a specific monomer, such as a 2-butanone oxime adduct, pyrazole adduct, or ε-caprolactam adduct of a ω-isocyanate alkyl(meth)acrylate, is used as the component monomer (b) in the copolymerization reaction.
Furthermore, the use of water- and oil-repellency processing treatment is extended to the outdoor field such as sportswear, and the water- and oil-repellency is required to be durable to repeated washing in such an application field. However, though the above-mentioned Patent Document 2 describes the water-dispersible water- and oil-repellent composition as that in which both the repeated washing resistance and the water resistance of water- and oil-repellency are achieved, a fluorine-containing copolymer including a perfluoroalkyl group having 6 or less carbon atom is not substantially used alone, and also the water-dispersible water- and oil-repellent composition can not impart sufficient water- and oil-repellency not only to synthetic fibers but also to natural fibers when it is used for water- and oil-repellency treatment.